1. Field of the Invention
This invention relates generally to linking members coupling a frame or structural member of a vehicle to a wheel housing. More specifically the present invention relates to a control arm used in an independent suspension system that provides sufficient flexibility when needed, yet provides adequate and increasing support during loading which otherwise may cause the control arm to buckle.
2. Description of the Related Art
In most vehicles today, the structural foundation is either a traditional frame, or unibody member. Most other components are then coupled or affixed to this foundation. Where unibody construction is used, subframe elements are often added to provide additional support and attachment points. For example, the vehicle's wheels are coupled to the structural foundation by a moveable support. The wheels can then be attached to this moveable support using a wheel drum as an intermediary. Many other components are similarly attached using appropriate attachment structures. Alternatively, this coupling can be connected directly to elements of the frame.
During movement or operation, various forces will be imparted on the vehicle. All of these forces will eventually be transferred to the subframe through all related components. In the case of the vehicle's suspension system, forces will be directed through the moveable support member, causing many different stresses and loads. These forces are most easily described with respect to the well understood orientation of the vehicle, where the frame or body is in a substantially horizontal position, with a centerline (or central axis) extending between the front and rear of the vehicle.
The most common forces a vehicle encounters is simply vertical displacement of the wheel housing. Such movement is induced by the vehicle encountering various bumps or obstacles in the road. These bumps or obstacles are expected and must be dealt with by the vehicle's suspension system. Since it is undesirable to impart this motion to the passenger cabin, various shock absorbers and springs are incorporated to deal with these forces. The link between the subframe and the wheel drum housing freely pivots in this direction thus causing substantially all vertical forces to be handled by the springs and shock absorbers.
Longitudinal forces are also imparted on the wheel housing as the vehicle travels. This results in various forces being presented to all components of the suspension. Lastly, tension loading occurs as force is applied to the wheel by pulling it away from the vehicle center line and transverse loading occurs in an opposite direction, pushing the wheel towards the center line of the vehicle.
In the vehicle's suspension system, all of the components must appropriately carry each of these loads. This load handling requirement is in addition to the basic function of attaching the wheels and allowing the vehicle to operate. Thus, each component of the system must be specifically engineered for its particular purpose, and must cooperate with all other components.
In a rear independent suspension system, the assembly coupling the wheel drum housing to the frame or rear cradle consists of a number of control arms. The control arms are required to accommodate all of the above-referenced forces encountered by the associated wheel. Vertical forces are primarily dealt with by springs and/or shock absorbers which cooperate with one or more of the control arms. As previously suggested, the control arms are hinged to allow free movement in the vertical direction. Thus, all vertical forces are transferred to the springs or shocks.
The wheel, as described, is also subjected to various longitudinal, transverse, and tensile forces. Various combinations of the forces imparted on the wheel will be applied to the control arms. The net result is that the control arms themselves will be subjected to longitudinal, transverse and tensile forces resulting from forces being applied to the wheel. Whatever force or combinations of forces is applied to the wheel (and wheel drum housing), the resultant force that is applied to each of the control arms must be appropriately handled by that component. As such, each control arm and its elastomer bushings are configured to handle the forces applied to it, dependent upon the direction of the force. It is to be understood that it is the resultant force that is applied to the control arm, in the longitudinal, tensile or transverse direction with respect to the part itself, that is being discussed with respect to the various responses that the control arm will achieve.
Tension loading forces (pulling away from the frame) are typically minimal and need not be considered separately, as longitudinal and transverse forces are the major considerations for the control arms. During longitudinal loading (which generates torque on the control arm), it is desirable to have soft torsional modes in the rear most control arm, which is also referred to as a suspension link. In other words, rigid resistance under longitudinal loading is undesirable, as this would cause these forces to be felt by the passengers. Therefore, if the suspension link is compliant and able to twist in response to the torque generated, the forces are absorbed and not passed on. Conversely, transverse loads (compression loads) (forcing the control arm towards the frame) can be rather extreme and could cause the suspension link to buckle. This makes it difficult to design a suspension link which is adequately compliant in the longitudinal direction and sufficiently strong in the transverse direction.
Various suspension systems have been provided to address the longitudinal forces imparted by a vehicle in motion. For example, U.S. Pat. No. 5,662,348 issued to Kusama et al. on Mar. 20, 1996, discloses a one-piece suspension arm wherein the portion of the suspension arm subject to the most longitudinal stress has been bent at each end to provide a more rigid frame. Kusama et al. utilizes less material, hence making the suspension arm lighter while imparting sufficient resistance to longitudinal forces. However, this design does not necessarily provide for the soft torsional bending which would be desirable in a suspension link. Furthermore, Kusama et al. fails to address the relatively high transverse forces which are also imparted.
As such, there exists a need to provide a control arm having soft torsional modes while providing adequate support during high transverse loading.